1. Field of the Invention
The invention relates generally to tubing conveyed perforator systems for perforating well casings, and more particularly to an expendable tubing conveyed perforator made from frangible and consumable materials. The invention also relates to methods of perforating well casings using an expendable tubing conveyed perforator made from frangible and consumable materials.
2. Description of the Art
Drilling of wells generally, and oil wells in particular, follows protocols that are well known in the industry. Conventionally, a hole is drilled into the earth where a reserve of useful fluid material, such as oil, gas, or water has been identified. A steel casing is next installed to line the hole and prevent the earth from filling the hole. The casing is then lined with a tube so that the material to be extracted may be conveyed to the surface. However, in order for the fluid material to enter the hole casing and be removed, it is necessary to perforate the casing.
Conventionally, perforation of the well casing is performed using a device termed a "tubing conveyed perforator" (TCP). The basic TCP unit consists generally of a 6-30 foot metal tube with a series of explosive charges placed along the centerline axis and pointing outward radially. The TCP is often made from a series of perforator unit segments that are connected together to form a desired length, often conforming to the width of the adjacent fluid reservoir. The TCP is lowered into the casing to the desired depth, and the charges are fired. The explosive force of the charges perforates the metal tube, the well casing, and the rock formation to produce holes in the rock formation that surrounds the fluid reserve. After firing, any remaining portion of the TCP is pulled out of the casing, and, if intact, can be reloaded with charges and reused. The fluids from the underground reserve flow or are forced through the newly formed holes in the casing, and into the extraction tube where they are collected and extracted.
However, the above method of perforating the well casing has several disadvantages. In many drilling situations, the post-fired metal tube that held the shaped charges cannot be removed from the hole without destroying the well. In these situations, expendable perforators are employed to fire the charges. Following firing, the expendable perforating system is dropped to the bottom of the drilled hole that extends below the targeted formation (known as the "rathole" portion of the well). However, formation of the "rathole" portion of the well requires additional drilling to depths as much as 2,000 feet beyond the target area so that the expended perforator can be accommodated. This extra drilling results in considerable additional time and drilling costs.
In addition, the conventional metal tubing used for the TCP generally fragments into large pieces of debris upon firing of the charges. These large pieces of metal debris often cause problems in fluid extraction, such as jamming of equipment, preventing tube removal, inhibiting fluid flow, contaminating the fluid, or clogging pumps or tubing used to extract the fluid.
One solution to these problems is described in U.S. Pat. No. 4,905,759 to Wesson et al., herein incorporated by reference in its entirety. The device described in this U.S. Patent utilizes spacer tubes between the TCP units that telescopically collapse lengthwise after firing. While this approach can reduce the required depth of the "rathole" and reduce drilling efforts, a significant portion of the rathole must still be drilled below the target depth. Moreover, debris from the expended TCP units are still capable of clogging oil pumping equipment and tubing, or jamming the device in the well casing thereby inhibiting oil flow. What is needed in the art is a tubing conveyed perforator that does not require substantial additional drilling and does not have the potential to clog oil extraction equipment with debris. The present invention is believed to be an answer to that need.